Conventionally, measured wheel rotation speeds are used as the basis for calculating vehicle speed. If the measurement occurs during deceleration of the vehicle simultaneously with engagement of an ABS antilock system, the wheel rotation speeds are affected by slip. If, in this situation, the brake pressure at individual wheels is at least slightly lowered, the wheel rotation speed that can be taken as the basis for calculating vehicle speed is thus increased. A prerequisite for this method, however, is that braking torques can be modulated at individual wheels of the vehicle, which is usually the case with hydraulic wheel braking devices.
In the case of braking devices that apply a braking torque via the drive train in the vehicle, for example during recuperative braking in hybrid or electric vehicles, or in the context of retarders in commercial vehicles, it is not possible to reduce the braking torque at only a single wheel in order to accelerate that wheel. On road surfaces having a low coefficient of friction, the result is that all the wheels are uniformly affected by brake slip, which can lead to a systematic error in calculating the vehicle speed. The calculated vehicle speed is lower than the actual speed, which can result in an overbraked vehicle with reduced steerability, and unstable vehicle behavior.